Eye tracking is the process to measure the eye movement or the eye-gaze direction. Various eye tracking technologies have been developed for use in a variety of applications, such as vision research, human computer interfaces, tele-surgery, product packaging, retail layout and advertising research, visual communication, and various military applications. One conventional method to track eye movement is to mount two cameras on a mount (e.g., a helmet), which capture images of each eye directly. This approach results in a bulky design and an unsightly appearance, which potentially may comprise research results.
In recent years, efforts have been made to design eyeglass like eye-tracking devices that are light, portable, ergonomic, and aesthetically more pleasing than previous technologies. For example, Tobii Technology of Stockholm, Sweden has developed an eye tracking system (www.tobii.com) that mounts the eye imaging camera on the arm of an eyeglass frame and captures an image of the eye through reflection off of the glass. The Tobii system has the advantage of an eyeglass like form factor, and is light weight, however, in order to properly capture the eye image through reflection off of glass, there must be sufficient clearance between the user's face and the glass surface to avoid the obstruction of the eye image by user's face or the imaging optics. This requires that very wide eyeglass lenses be used to avoid interference between the imaging path and any part of the user's face. The resulting overall package does not resemble a conventional pair of eyeglasses, and as a result, test subjects are unlikely to use the Tobii product outside of a laboratory environment.
Similarly, SensorMotoric Instruments GmbH or Teltow, Germany (“SMI”) has developed an eye tracking system (www.smivision.com), which also has an eyeglass like appearance and is lightweight. In the SMI system, the camera is mounted on the glass frame under the eye, and directly images the eye. This results in a thick and bulky frame design, which must move the camera far enough away from the face to avoid interference. Furthermore, in this system, the camera captures an eye image at a close distance and from a slanted direction (i.e., at a high angle), which results the eye image suffering keystone distortion. This arrangement also presents optical performance challenges due to the large depth of field necessary to accommodate all possible eye positions.
U.S. Pat. No. 6,735,328 discloses the use of a beamsplitter immersed in an eyeglass lens, off of which an eye is imaged by a vertically oriented camera positioned above a user's line of sight. While the arrangement of this patent is an improvement over other designs discussed above, the field of view of the camera in this arrangement is severely limited by the disclosed geometry.
U.S. Pat. No. 6,943,754 discloses an eye tracking system including a camera. The camera images an eye using a bulky and unsightly visor that hangs in front of the face of a user.
U.S. Pat. No. 8,398,239 discloses providing an array of optical detection elements directly onto an eyeglass like lens located in front of an eye. While this device appears to be somewhat similar to a pair of eyeglasses in form factor, it is necessarily expensive and complex to fabricate, as it requires the use of semi-conductor fabrication processes to fabricate optical detectors and their associated electronics on a curved glass lens substrate.